Valve train friction is a significant fraction of total engine friction. It is therefore desirable to reduce the frictional work between the sliding parts of the engine valve train to improve the fuel efficiency of the engine. Because of the necessity to control oil flow past the valve guides, and also because the valve stems are hot, the lubrication conditions between valve stems and valve guides are typically marginal, and the friction between these sliding parts is Coulomb friction. A reduction in the side loads on the valve stem with respect to the valve guide will produce a proportionate reduction in this friction, and will also reduce valve guide wear. Reduction in side loads will also make it possible to install more restrictive valve guide seals. It is the purpose of the present invention to radically reduce the side forces on the valve stem due to actuation of the valve by the rocker tip. Although the frictional work in sliding between a conventional rocker tip and the valve stem is not in itself large, the frictional work produced by side forces on the valve is significant. The wear problem is similarly significant.
The sliding velocities between a rocker tip and the valve tip are very small even at high engine speeds, and the contact pressures are high. However, the valves in an internal combustion engine are only actuated approximately 30 percent of the time, and are unloaded otherwise. This is an ideal situation for squeeze film lubrication, since there is a significant amount of time available for replenishing an oil film between load applications which squeeze the oil film out from between the sliding surfaces. By maintaining a squeeze film between the rocker tip and the valve tip, the side friction forces of rocker tip actuation on the valve stem can be reduced by more than a factor of 100, producing corresponding reductions in valve actuating friction and reductions in valve guide wear.